Recording materials based on a color forming reactions between a coloring chromogen and a developer allow them to record by a relatively simple device in a short time without troublesome processes such as development and fixing. They are thus used widely as thermal recording paper for output recording from FAX and printers or as carbonless paper for accounting cards in order to make several copies at once. There is a demand for recording materials which can develop colors promptly, prevent a color change in the non-image area (hereinafter referred as background) and maintain the colored (recorded) images and background firmly. Furthermore, a large number of recording materials have been used in recent years in the fields where the reliability of recorded images are very important, such as labels. Required are recording materials with high preservability against plasticizers and oils contained in organic polymer materials used for packaging. Therefore effort has been made to develop various auxiliary agents such as coloring chromogens, developers and stabilizers. Fully satisfactory materials have not been found yet. Compounds having a structure of diphenyl sulfone crosslinking, which are similar to those of the present invention, are disclosed in Japanese patent laid-opened Nos. Hei 5-194368 and Hei 5-310683, as well as Japanese Patent Laid-Opened Hei 7-149713 and World opened W093/06074 and WO95/33714. These compounds are hardly satisfactory from the viewpoint of high recorded image preservability.
Improvements in recording materials are wanted in the preservability of colored images, and particularly in recent years in resistance against plasticizers, oils, light, humidity and heat. It is an object of the present invention to provide recording materials with excellent preservability of colored images in order to solve the problems mentioned above.